Electroplating process



2,830,014 Patented Apr. 8, 1958 ice 2,830,014 ELECTROPLATING PROCESS Wolfgang Giindel, Wennemar Strauss, and Herman Haas, Dusseldorf, Germany, assignors to Dehydag,

. Deutsclre Hydrierwerke G. m. b.'H., Dusseldorf, Germany, a corporation of Germany No Drawing. Application October 25, 1954 Serial No. 464,638

Claims priority, application Germany March 22, 1954 16 Claims. 01. 204-49 7 This invention relates to an electroplating process, and

more' particularly to such aprocess employing derivatives of organic sulfonic acids as brightening agents.

Electroplating baths have heretofore been modified by the inclusion of organic sulfonic acids or organic sulfation products of various compounds. While the prior art brightening agents have usually elfected some improvement in the brightness characteristics and ductility of electrodeposits products from baths modified therewith, these brightening agents individually have not been sufficient to produce commercially desirable electrodeposits, and have to be used with another and sometimes with even two or more supplemental brightening agents to produce the desired result.

It is, therefore, an object of this invention to provide brightening agents for electroplating fbaths which may advantageously be used as a sole brightening agent or with other addition agents to produce bright and ductile electrodeposits.

Another object of our invention is to provide electroplating compositions of improved character.

Still another object of our invention is to provide electroplating baths which will produce bright, lustrous and ductile electrodeposits which in many instances may be used for their'intended purpose without further polishing or butting.

Still further objects and advantages of our invention will become, apparent as the description thereof proceeds. We have-found that the brightness and ductility of metal electrodeposits can be materially improved, particularly in case of nickel electrodeposits, by adding to such electroplating baths small amounts of organic sulfonic acid compounds having the general structural formulas wherein R-ishydrogen or an acyclic or cyclic hydrocarbon radicaL'Y is a lower alkylene, CSNH, CSNH-phenyl, CO, CS 'or S group, .R is a bivalent hydrocarbon radical, and X is hydrogen or an inorganic or organic basic substituent; Hydrocarbon radicals R and R may also be interrupted by oxygen, sulfur or nitrogen atoms or hetero atom groups derived therefrom, and may in addition contain substituents composed of hetero atoms or hetero atom groups.

The class of compounds having the above general structural formula consists essentially of well-known substances which may be produced very readily. For example, they can be obtained in a very simple manner and in a high degree of purity by reacting metal sulfides, metal hydro sulfides, or the salts of aliphatic, cycloaliphatic, aromatic-aliphatic, aromatic heterocyclic mercapto compounds, or metal compounds of dithiolic acids, thiol acids or thioamides with cyclic anhydrides or organic oxyalkanesulfonic acids (sultones), such as for example,

l,3-propane.sultone, 1,4-butane sultone, etc.

Another method of producing the above sulfonic acid compounds is to react the sulfur-containing compounds referred to in the preceding paragraph with halogenalkanesulfonic acids or their salts rather than with sulitonesr In a few cases itisalso possible to start with mercapto-alkane-sulfonic acid salts by reacting the same with corresponding halogen compounds.

Examples of thioalkanesulfonic acids having the general structural formula referred to which can be prepared by any of the above methods and may then be added to electroplating baths as brightening agents and as agents which promote the increase of the ductility of metal electrodeposits produced from such baths in accordance with our invention are the following:

.Phenylthiopropane-w-sodium sulfonate 4-bromophenylthioethane-w-sodium sulfonate Furfuryl-thiopropane-w-sodium sulfonate Thioacetic acid-S-propylester-w-sodium sulfonate Thiobenzoic acid-S-propylester-w-sodium sulfonate Methyl-dithiolic acid-propylester-w-sodium 'sulfonate .Phenyl-dithiolic acidpropylester-w-sodium sulfonate Phenylsulfothiolic acid-propylester-w-sodium sulfonate Thioacetamide-S-propanew-sodium sulfonate Thioacetanilide-S-propanew-sodium sulfonate Thiobenzamide-S-butane-w-sodium sulfonate The brightening and ductility-improving agents of our invention can be employed to modify electroplating baths of all types. Thus, they will produce the desired effects in copper-plating, zinc-plating, silver-plating, nickel-plating, brass-plating and other such metal-plating baths, regardless of whether the metal plate is deposited by means of an electric current or merely by dipping the objects to be plated into the'plating bath. v

Moreover, the compounds or" our invention can beem- 'ployed in conjunction with other well-known brightening agents, conductivity-promotingsalts, wetting agents, porosity-preventing agents, smoothing agents, and the like.

The amounts in which the thioalkanesulfonic acids, in accordance with our invention, are added to electroplating baths in order to produce bright and highly ductile metal electrodeposits range from 0.01 to 20 grams per liter of electroplating bath, depending upon the particular additive used and the type of metal which is intended to be electrodeposited. In general, the temperature of electroplating baths modified in accordance with our invention should be about 60 C. during the electroplating operation and the current density range should be between 0.5 and 1 2 amp./dm. The current density which will produce the optimum brightening eifect depends upon the individual thioalkanesulfonic acid additive used to modify the electroplating bath in accordance with our invention.

The addition of the thioalkanesulfonic acid compounds as disclosed by us does not require changes in the operating conditions commonly employed in electroplating processes. V

The surfaces of the objects to be electroplated in. electroplating baths modified in accordance with our .inven- 'tion may consist of any type of metal or alloy upon. which electroplates are usually deposited. In the case where the metal surface consists of steel, iron, zinc, and other non- 3 precious metals or their alloys, it is recommended that such surfaces be covered with a thin layer of copper in the customary cyanide-copper sulfate solution prior to plating such surface with the final metal electroplate.

Electrodeposits produced from plating baths modified with the thioalkanesulfonic acids or their salts in accordance with our invention are extremely bright, adhere well to the base surface, have a high degree of ductility and are practically free from porosity. Their brightness is in most cases so high that subsequent polishing and buffing is not required.

The thioalkanesulfonic acid additives of our invention are extremely stable in acid solutions, so that electro-- plating baths modified therewith remain capable of producing bright and duticle electrodeposits for extended periods of time even at high temperatures, and need to be rejuvenated only from time to time with small amounts of these additives.

The following examples will serve to illustrate our invention more clearly and enable persons skilled in the art to understand our invention more completely. However, it is understood that our invention is not intended to be limited to the scope of theexamples which follow.

Example I nickel sulfate and 35 gm./liter boric acids Sheet steel which was pre-treated in a well-known manner in a copper sulfate-cyanide bath by dipping it therein in order to deposit a thin preliminary copper plate on the surface,

was then nickel-plated in the modified bath at room temperature and a current density of 5 amp./dm. The nickel plate thus produced was fine-bright, well-adhering and free from porosity, and required no further mechanical treatment such as buffing or polishing.

In place of 3-mercaptopropane-1-sodium sulfonate, the di-sodium salt of di-n-propylthioether-w-w-disulfonic acid can be used with equal success.

Example II:

1.5 gm./liter of phenylthiopropane-w-sodium sulfonate were dissolved in a nickel-plating bath which contained 60 gm./liter nickel chloride, 120 gm./liter crystallized nickel sulfate and gm./ liter boric acid. Sheet steel, which was pre-treated as in Example I, was then nickel-plated in the modified plating bath at room temperature and a current density of 5 amp./dm. The nickel plate thus produced was fine-bright and highly ductile and required no additional polishing or bufling.

The same results were obtained when 1.25 gun/liter thioacetanilide-S-propane-w-sodium sulfonate were substituted for phenylthiopropane-w-sodium sulfonate.

Example 111 Example 1V 1 gm. of dithiobenzoic acid-n-propylester-w-sodium sultonate was added to each liter of a zinc galvanizing bath containing 60 gm./ liter zinc cyanide, 50 gm./liter sodium cyanide, l5 gm./liter sodium hydroxide and 1 gm./liter sodium sulfite. Metal objects were then zinc-plated in this modified bath at room temperature and a current density between 2 and 10 ampJdmF. The zinc plate produced thereby was fine-bright and adhered very well to the metal surface.

Equally good results can be obtained when, in place of the dithiobenzoic acid salt referred to above, an equal amount of thiobenzamide-S-propane-w-sodium sulfonate is used as a brightening agent.

Example V A small amount of S-benzyl-3-thiopropane 1-sodium sulfonate was added to an acid copper-plating bath which contained 220 gm./liter copper sulfate and 60 gm./liter sulfuric acid. Objects were then copper-plated in this modified bath at room temperature and a current density of 5 amp./dm. The copper depositsproduced thereby were bright, soft and had an extremely fine grain.

While we have. disclosed certain specific embodiments of our invention, we wish it to be understood that said invention is not limited to such embodiments, and that changes and variations may be made therein without departing from the spirit of our invention or the scope of the appended claims.

We claim: I p

1. An electroplating bath for producing electro-deposits of a metal selected from the group consisting of copper,

zinc and nickel, comprising an acid solution of at least one inorganic salt of the metalto be electrodeposited and from 0.01 to 20 gm./liter of a sulfonic acid compound having a structural formula selected from the group consisting of 2. An electroplating bath for producing electro-de positsof a metal selected from the group consisting of copper, zinc and nickel, comprising an acid'solution of at least one inorganic salt of the metal to be electrodeposited and from 0.01 to 20 gm./liter of a compound selected from the group consisting of sulfonic acids having the structural formula and their alkali metal salts, wherein R is acyclic nonheterocyclic hydrocarbon radical, Y is selected from the group consisting of lower alkylene, -CSNH, -CSNH- phenyl--, -C0, -CS, and SO and R is a lower alkylene radical. r

4. An electroplating bath for producing electrodeposits of nickel, comprising an acid solution of at least one inorganic salt of nickel and 0.01 to 20 -gm./liter of the disodium salt of di-n-propylithioether-w-w-disulfonic acid.

5. An electroplating bath for producing electrodeposits ,of ,zinc comprising an acid. solution of at least one inorganic salt of zinc and 0.01 to 20 gm./liter of dithiobenzoic acid-n-propylester-w-sodium sulfonate.

6. An electroplating bath for producing electrodeposits of zinc comprising an acid solution of at least one inorganic salt of zinc and 0.01 to'20 gm./liter of thiobenzamide-S-propane-w-sodium sulfonate.

7. An electroplating bath for producing electrodeposits of copper comprising an acid solution of at least one inorganic salt of copper and 0.01 to 20 gm./liter of S- benzyl-3-thiopropane-l-sodiurn sulfonate.

8. An electroplating bath for producing electrodeposits of nickel comprising an acid solution of at least one inorganic salt of nickel and 0.01 to 20 gm./liter of phenyl-thiopropane-w-sodiurn sulfonate.

9. The process of producing bright and lustrous electrodeposits of a metal selected from the group consisting of copper, zinc and nickel, which comprises electrodepositing said metal from a bath containing said metal principally in the form of an acid solution of an inorganic salt of the metal in the presence of from 0.01 to 20 gm./liter of a sulfonic acid brightening agent having a structural formula selected from the group consisting of and their alkali metal salts, wherein R is selected from the group consisting of hydrogen, acyclic hydrocarbon radicals and cyclic non-heterocyclic hydrocarbon radicals, R is a lower alkylene radical, and Y is selected from the group consisting of lower alkylene, -CSNH-, -CSNH-phenyl, -CO--, -CS- and SO 10. The process of producing bright and lustrous electrodeposits of a metal selected from the group consisting of copper, zinc and nickel, which comprises electrodepositing said metal from a bath containing said metal principally in the form of an acid solution of an inorganic salt of the metal in the presence of from 0.01 to 20 gm./liter of a brightening agent selected from the group consisting of sulfonic acids having the structural formula and and their alkali metal salts, wherein R is an] acyclic I and their alkali metal salts, wherein R is a cyclic nonheterocyclic hydrocarbon radical, Y is selected from the group consisting of lower alkylene, CSNH-, CSNH- phenyl--, CO-, CS and SO,;, and R is a lower alkylene radical.

12. The process of producing bright and lustrous nickel electrodeposits which comprises electrodepositing said nickel from a bath containing said nickel principally in the form of an acid solution of at least one inorganic salt of nickel, in the presence of 0.01 to 20 gm./liter of the disodium salt of di-n-propylthioether-w-w-disulfonic acid as a brightening agent. t

13. The process of producing bright and lustrous zinc electrodeposits which comprises electrodepositing said zinc from a bath containing said zinc principally in the form of an acid solution of at least one inorganic salt of zinc, in the presence of 0.01 to 20 gm./liter of dithiobenzoic acid-n-propylester-w-sodium sulfonate as a brightening agent.

, 14. The process of producing bright and lustrous zinc electrodeposits which comprises electrodepositing said zinc from a bath containing said zinc principally in the form of an acid solution of at least one inorganic salt of zinc, in the presence of 0.01 to 20 gm./liter of thiobenzamide-S-propane-w-sodium sulfonate as a brightening agent.

15. The process of producing bright and lustrous copper electrodeposits which comprises electrodepositing said copper from a bath containing said copper principally in the form of an acid solution of at least one inorganic salt of copper, the presence of 0.0lto 20 gm./liter of S-benyl-3-thiopropane-l-sodium sulfonate as a brightening agent.

16. The process of producing bright and lustrous nickel electrodeposits which comprises electrodepositing said nickel from a bath containing said nickel principally in the form of an acid solution of at least one inorganic salt of nickel, in the presence of 0.01 to 20 gm./liter of .phenylthiopropane-w-sodium sulfonate as a brightening agent. 7

References Cited in the file of this patent UNITED STATES PATENTS 2,647,866 BI'OWII Aug. 4, 1953 

1. AN ELECTROPLATING BATH FOR PRODUCING ELECTRO-DEPOSITS OF A METAL SELECTED FROM THE GROUP CONSISTING OF COPPER, ZINC AND NICKEL, COMPRISING AN ACID SOLUTION OF AT LEAST ONE INORGANIC SALT OF THE METAL TO BE ELECTRODEPOSITED AND FROM 0.01 TO 20 GM./LITER OF A SULFONIC ACID COMPOUND HAVING A STRUCTURAL FORMULA SELECTED FROM THE GROUP CONSISTING OF 